The present invention relates to a self-propagating high temperature synthesis (SHS) process for making highly pure powder alloys of cadmium and selenium, optionally ternary or quaternary alloys with other elements, with or without dopants, for use in vapor deposition processes for photovoltaic devices.
During the fabrication of photovoltaic devices, layers of semiconductor material can be applied to a substrate with one layer serving as a window layer and a second layer serving as the absorber layer. The window layer allows the penetration of solar radiation to the absorber layer, where the optical power is converted into electrical power. Some photovoltaic devices use transparent thin films that are also conductors of electrical charge. The conductive thin films may include transparent conductive layers that contain a transparent conductive oxide (TCO), such as fluorine-doped tin oxide, aluminum-doped zinc oxide, or indium tin oxide. The TCO can allow light to pass through a semiconductor window layer to the active light absorbing material and also serve as an ohmic contact to transport photogenerated charge carriers away from the light absorbing material. A back electrode can be formed on the back surface of a semiconductor layer. The back electrode can include electrically conductive material, such as metallic silver, nickel, copper, aluminum, titanium, palladium, chrome, molybdenum or any practical combination thereof. Methods for forming such semiconductor layers include vapor deposition and/or sublimation of metal alloys from a power alloy product.
Known prior art processes for making alloy powders include High-pressure Bridgman (HPVB) and vertical zone melting (HPVZM) growth processes, both of which are described in Kolesnikov, et al., Brookhaven National Laboratory Report BNL-69260 (2002), incorporated by reference. For example, the paper describes manufacturing Cd(1-x)ZnxTe (x=0.04-0.2), CdSe and ZnSe crystal tapes with sizes up to 120×120×12 mm. The influences of the technological parameters describing the growth processes on the crystal quality and some selected material properties are discussed in this paper. However, the HPVB and HPVZM methods require specific high-pressure reactors that are expensive equipment.
It would be advantageous if there could be developed highly pure alloys in powder form for use in vapor deposition or sublimation processes for thin film photovoltaic cells.